Method of reducing gels in polyolefins

a polyolefin and gel technology, applied in the field of reducing the number of gels in polyolefins, can solve the problems of reducing the value of these films, affecting the marketability of films, and common presence of gels

Active Publication Date: 2008-07-01
UNIVATION TECH LLC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The presence of “gels” is a common problem in polyolefins.
The presence of gels lowers the value of these films, and in some cases makes the films unmarketable.
However, there are no specific solutions to removing gels common in polyolefin melts, especially polyethylene melts and bimodal or multimodal polyethylene melts.
These solutions are both somewhat inadequate because the first requires multiple active screens, increasing cost and complexity as well as being limited to polypropylene in its usefulness, while the second approach has the problem of high pressure drop and propensity for screens to plug quickly.

Method used

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  • Method of reducing gels in polyolefins
  • Method of reducing gels in polyolefins
  • Method of reducing gels in polyolefins

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0066]Compares 20, 200, and staged 325 mesh. Polyethylene granules were extruded into pellets either without any additives, or and blended with the following additives (“Formula A”):

[0067]

Irganox-10100.1500 wt %Irgafos-1680.1500 wt %Zinc Stearate0.0500 wt %

These pellets were used to form the films. General conditions for the extrusion into pellets are as follows:

[0068]Barrel temperature set point, 180° C.

[0069]Ambient feed temperature.

[0070]Less than 1% oxygen.

[0071]Mixer speed, 220 rpm.

[0072]Mixer feed rate, 410 lbs / hr.

[0073]Gate position, 5%.

[0074]Melt pump suction pressure, 7 psig.

[0075]Screen changer with a 4.5 inch diameter the breaker plate.

[0076]See Tables 1 and 2 for the conditions of pelletizing and film extrusions, respectively. FIG. 1 shows the gel count results. Data for 20 mesh were from a single condition, data for 200 mesh are the average of 8 conditions and 8 gels counts, data for triple 325 mesh are the average of 2 conditions and 2 gel counts. See Table 1 for an ex...

example 2

[0078]Compares no screen, 200 mesh, and staged 250 mesh. See Example 1 for a description of the additives used to form the pellets and general extrusion conditions. All data are from single extended extrusion conditions. See Tables 3 and 4 for the conditions of pelletizing and film extrusions, respectively (“G / P” refers to gear pump). FIG. 2 shows the gel count results. Surprisingly, a single 200 mesh screenpack (20 / 100 / 200 / 100 / 20 mesh) reduced gels as well as a screenpack with two 250 mesh screens (20 / 100 / 250 / 100 / 250 / 100 / 20 mesh).

example 3

[0079]Compares no screen, 100, 150, 200, and staged 250 mesh. See Example 1 for a description of the additives used to form the pellets and general extrusion conditions. All data are from single extended extrusion conditions. 100 and 150 mesh performed surprisingly well. See Tables 5 and 6 for the conditions of pelletizing and film extrusions, respectively. FIG. 3 shows the gel count results.

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Abstract

A process of producing a polyolefin, in one embodiment a polyethylene, and in a preferred embodiment a bimodal polyethylene comprising a high molecular weight component and a low molecular weight component, the process comprising providing a polyolefin having an I21 value of from 2 to 100 g / 10 min and a density of from 0.91 to 0.97 g / cm3; followed by forming a melt of the polyolefin and passing the polyolefin through one or more active screen filter(s) having a mesh size of from 70 to 200 micron at a mass flux of from 5 to 100 lbs / hr / square inch; and isolating the polyolefin having passed through the screen filter.

Description

FIELD OF THE INVENTION[0001]The present invention relates to methods of reducing the number of gels in polyolefins, and more particularly to a method of melt extruding polyethylene compositions through one or more active screen(s) in order to lower the number of gels in the melt and form a film having improved film appearance.BACKGROUND OF THE INVENTION[0002]The presence of “gels” is a common problem in polyolefins. The term “gels” refers to highly localized imperfections in the polyolefin, especially film made from polyolefin, that are visually distinct from the surrounding film, mostly due to the presence of either high concentrations of unblended polymer, unreacted catalyst and activator, or both, but can include other types of visually distinct imperfections as well. The presence of gels lowers the value of these films, and in some cases makes the films unmarketable. There have been many approaches in the past to solving this problem. One approach is to remove the gels prior to ...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): C08F6/00
CPCC08F6/26C08L23/06C08L2205/02C08L2205/025C08L2308/00C08L2666/06C08F10/00C08F6/16
Inventor NEUBAUER, ANTHONY CHARLESEHRMAN, FRED D.TUNNELL, III, H. RODNEY
Owner UNIVATION TECH LLC
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